kernel: use LcmInt in order computations, fix GC bugs

[fingolfin]

The order computation for permutations, partial permutations and
transformations now uses LcmInt(). Also, fixed a garbage collection related
bug in each: a GC could invalidate pointers to a temporary object

[codecov]

Codecov Report

Merging #2154 into master will increase coverage by 0.03%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #2154      +/-   ##
==========================================
+ Coverage   69.34%   69.38%   +0.03%     
==========================================
  Files         484      485       +1     
  Lines      253917   255428    +1511     
==========================================
+ Hits       176085   177225    +1140     
- Misses      77832    78203     +371

Impacted Files	Coverage Δ
src/integer.h	100% <ø> (ø)	⬆️
src/pperm.c	83.66% <100%> (+0.05%)	⬆️
src/permutat.c	78.02% <100%> (-0.03%)	⬇️
src/trans.c	98.72% <100%> (-0.01%)	⬇️
src/hpc/guards.h	80.55% <0%> (-11.45%)	⬇️
src/debug.c	26.92% <0%> (-9.92%)	⬇️
src/hpc/thread.c	51.48% <0%> (-4.23%)	⬇️
src/hpc/aobjects.c	67.4% <0%> (-4.22%)	⬇️
hpcgap/lib/hpc/queue.g	66.4% <0%> (-3.2%)	⬇️
src/hpc/aobjects.h	84.61% <0%> (-2.89%)	⬇️
... and 39 more

[markuspf]

Good catch...